Apparatus for forming deposited film

ABSTRACT

An apparatus for forming a deposited film comprises a chamber, which can be brought into a reduced pressure, for forming a deposited film on a substrate by introducing a starting gas into said chamber and decomposing or polymerizing said gas, the apparatus is provided with both a means for decomposing or polymerizing said gas by discharging and a means for decomposing or polymerizing said gas by heat.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus for forming a deposited film, forexample, a deposited film of an amorphous material comprising siliconatoms as the main component (hereinafter abbreviated as a-Si), etc. on asubstrate.

2. Description of the Prior Art

In the following, this type of technique is explained by referring to anembodiment employing a-Si for an electrophotographic photosensitivemember.

Generally speaking, an electrophotographic photosensitive member isconstituted by laminating various kinds of functional layers such asphotoconductive layer, charge injection preventive layer, protectivelayer, etc. on a substrate having a desired shape such as cylinder, etc.Of such electrophotographic photosensitive members, theelectrophotographic photosensitive member employing a-Si as thefunctional layer as mentioned above is attracting attention as asubstitute for the electrophotographic photosensitive member employingan amorphous selenium of the prior art for the various advantagespossessed by a-Si, for example, little change with lapse of time, noenvironmental contamination, high surface hardness, etc.

FIG. 2 is a schematic illustration of the structure of a typical exampleof such an electrophotographic photosensitive member employing a-Si.

In FIG. 2, 1' is a substrate which is usually made of an aluminum drum.2' is a charge injection preventive layer which prevents injection ofcharges from the substrate 1' into the photoconductive layer 3' andlaminated on the substrate 1'. For example, when charging is effected bycorona charging of ⊕ polarity, it is necessary to prevent injection of ⊖charges from the charge injection preventive layer 2' into thephotoconductive layer 3'. Ordinarily, the charge injection preventivelayer 2' is constituted of a-Si doped with elements having trivalentvalance such as boron (B) (the layer is of P⁺ a-Si), in which a mobilityof electrons is made smaller by said elements to effect injectionprevention of charges.

On the charge injection preventive layer 2' is laminated aphotoconductive layer 3', which is ordinarily constituted of a non-dopeda-Si layer. On this photoconductive layer 3' is further laminated aprotective layer 4' to constitute an electrophotographic photosensitivemember. The protective layer 4' is provided for further improvement ofdurability, and this is ordinarily constituted of an a-Si with broadband gap containing carbon (C) atoms (a-SiC layer). Thus, theconstitution of an electrophotographic photosensitive member isgenerally made a four layer constitution of Al/P⁺ a-Si/non-dopeda-Si/a-SiC.

The respective functional layers of such a photosensitive member aregenerally prepared according to the plasma decomposition methodutilizing flow discharging. However, the plasma decomposition methodinvolves the problems as mentioned below, and such problems areparticularly marked in the case of preparing a layer with a thick layerthickness such as non-doped a-Si layer, which requires a layer thicknessof about 20 μm or more.

That is to say, (1) the gases such as SiH₄, Si₂ H₆, etc. used as thestarting gas tend to spontaneously combust, and film preparation isaccompanied with danger and disposal of waste gases; (2) whiledecomposition efficiency of the starting gas is required to be increasedin order to increase the film deposition speed, the applied voltage mustbe made higher for this purpose, but increased applied voltage willinevitably result in increase in species of radicals or ions generatedby decomposition of the starting gas, whereby those having deleteriouseffects on the film characteristics may also be increased; (3) forobtaining uniform film characteristics, discharging is required to beeffected uniformly, but such control of discharging is difficult for aproduct with large area such as an electrophotographic photosensitivemember.

Methods which have been proposed for preparing an electrophotographicphotosensitive member having excellent film characteristics bycancelling such problems are the so called pyrolysis methods in whichradicals are formed. Among these, the method for preparing non-dopeda-Si layer photoconductive layer through utilization of the pyrolysisreaction: ##STR1## is a method excellent with respect to safety, because(CH₃)₃ SiH and (CH₃)₃ Si₂ H₃ are gases that do not spontaneouslycombust. It has also the advantages that film characteristics are easilycontrolled due to relatively limited species of radicals being generatedin the pyrolysis method as compared to the plasma decomposition method,as well as high film deposition speed. It is also possible to prepare P⁺a-Si layer by using in the pyrolysis reaction a gas for doping such asB₂ H₆, etc. The film characteristics of these functional layers havebetter quality than those obtained by the plasma decomposition method.

However, concerning a-SiC layer, it has been difficult to prepare thisaccording to the pyrolysis method, since both SiH₂ and CH₂ cannot beformed into the layer.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of the variouspoints as described above, and an object of the present invention is tocancel the problems in the prior art examples and provide a novelapparatus for forming a deposited film which is capable of forming adeposited film through utilization of both decomposition orpolymerization utilizing heat and decomposition or polymerizationutilizing discharging.

Another object of the present invention is to provide an apparatus forforming a deposited film comprising a chamber, which can be brought intoa reduced pressure, for forming a deposited film on a substrate byintroducing a starting gas into said chamber and decomposing orpolymerizing said gas, said device being provided with both a means fordecomposing or polymerizing said gas by discharging and a means fordecomposing or polymerizing said gas by heat.

Still another object of the present invention is to provide a method forforming a deposited film on a substrate which comprises forming a partof said deposited film by decomposition or polymerization of thestarting gas by heat and forming at least a part of the remainder of thedeposited film by decomposition or polymerization of the starting gas bydischarging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the structure of an embodiment ofthe apparatus of the present invention; and

FIG. 2 is a schematic sectional view of a typical example of theconstruction of the electrophotographic photosensitive member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, the present invention is to be described indetail.

FIG. 1 is a schematic illustration of the construction of an example ofthe device of the present invention.

As shown in FIG. 1, the apparatus of the present invention is providedwith six vacuum compartments shown by 1-6 adjacent to each other, eachof which can function as an independent chamber. Between the respectiveadjacent compartments are provided gate valves freely openable by themechanism not shown so that each chamber may function internally as achamber independent of each other. Also, in each of these vacuumcompartments, there is provided an evacuation system comprising rotarypump, diffusion pump, etc. (not shown) so as to maintain the pressure ineach compartment at a desired level independently of each other.Compartments, 3 and 5 are vacuum compartments to be used as thedeposition chambers for carrying out film formation, 3 being acompartment for carrying out film formation by utilization of heat and 5being a compartment for carrying our film formation by utilization ofdischarging 1, 2, 4 and 6 are vacuum compartments (hereinafter calledpreliminary compartments) provided for delivering a substrate (in thisexample, Al drum 60 for electrophotographic photosensitive member) intoand out of the compartment 3 and the compartment 5, and no filmformation is conducted in these preliminary compartments.

The gate valves provided between the respective compartments function asthe partition walls for separating the vacuum compartments from eachother and also as the inlet or outlet for delivering the drum into orout of the respective compartments, and therefore should preferably bemade of a system capable of automatic opening and closing.

Referring now to an example of the case of forming deposited films incompartments 3 and 5, repsectively, by delivering a drum 60 from theprelilminary compartment 1 into the device, and subsequently moving thedrum in the order of the preliminary compartment, the compartment 3utilizing heat for film formation , the preliminary compartment 2, thepreliminary compartment 4, the compartment 5 utilizing discharging forfilm formation, the preliminary compartment 4, and the preliminarycompartment 6, the constitutions and functions of the respectivecompartments are to be described. Of course, the order of drum movementis not restricted to this order, but various modifications may bepossible. For example, the preliminary compartment 6 may be made thepreliminary compartment for delivering the drum into the apparatus, andit is also possible to repeat film formation between the compartment 3utilizing heat for film formation and the compartment 5 utilizingdischarging for film formation, depending on the properties to belaminated. For example, as embodiments of the method of the presentinvention, first film formation is performed by utilization of heat, andthen film formation by utilization of discharging; or alternatively filmformation is performed by utilization of heat, then film formation byutilization of discharging and further film formation by utilization ofheat; or other various procedures including the reversed orders of theseprocedures may be considered. These procedures can be selected optimallydepending on the type of the deposited film, the layer constitution,etc.

Delivery of the drum into the preliminary compartment 1 may be donethrough the freely openable door 101. For delivery of the drum, a drumdelivering means such as hoist, not shown in the drawing, is employed.The drum delivered from outside of the system is placed on the beltconveyer 102. The conveyer 102 is a delivering means for drum movementwithin the preliminary compartment 1 and drum delivery into thepreliminary compartment 2, and it is made freely rotatable. Afterdelivery of the drum into the compartment, with the preliminarycompartment 1 having the door 101 and the gate valve 12 closed, thepreliminary compartment is internally evacuated. The evacuationoperation is performed every time when the drum is delivered into thecompartment, and the drum transfer is done wheh the pressure in thepreliminary compartment 1 becomes approximately the same as that in thepreliminary compartment 2. Transfer of the drum to the preliminarycompartment 2 is performed by opening the gate valve 12 after completionof evacuation and transferring the drum from the conveyer 102 to thesimilar conveyer 201 to 102 provided in the preliminary compartment 2.

The drum delivered into the preliminary compartment 2 is suspended onthe hoist 206 which is the drum delivering means for delivering the druminto compartment 3 in which layer formation is conducted by utilizationof heat. 202 is a hanging metallic member which is the drum suspendingmeans provided on said hoist. Drum transfer to the compartment 3utilizing heat for film formation is performed by opening the gate valve23, with the gate valves 12 and 24 closed.

The evacuation operation in the preliminary compartment 1 is required tobe performed every time when the drum is delivered, because the drum isdelivered from outside into the preliminary compartment 1. However, drumdelivery from the preliminary compartment 1 to the preliminarycompartment 2 is conducted while maintaining the pressure within thesystem, and therefore it is possible to transfer the drum from thepreliminary compartment 2 to the compartment 3 while maintaining thepreliminary compartment 2 under vacuum condition. Accordingly, duringfilm formation, the next drum can be delivered into the preliminarycompartment 1 and the compartment 1 evacuated, and then it is possibleto deliver the next drum immediately after transfer of the drum afterfilm formation into the compartment 3 where film formation is conductedby utilization of heat, whereby evacuation operation requiring a longtime can be shortened to improve productivity.

The drum delivered into the compartment 3 utilizing heat for filmformation is set in close contact with the heat sink drum not shown inthe drawing which is the drum holding means. The heat sink drum isequipped with a cooling tube through which cooling water for drumcooling is passed and a heater for drum heating, and the drumtemperature is controlled by said cooling tube and heater The startinggas is introduced into the compartment 3 through a gas introducing pipe33. The gas introducing pipe 33 is equipped with gas charging orificesthrough which gas is uniformly charged onto the drum. The starting gascharged into the compartment 3 is decomposed by heating by IR-ray lampwhich is the gas heating means at a temperature of the decompositiontemperature of said gas or higher. The gas decomposed by heating isattached on the drum to form a deposited film from said gas as thestarting material on the drum. 32 is a reflection mirror which condensesIR-ray emitted from the IR-ray lamp 31 for improvement of heatingefficiency of the IR-ray lamp and is provided to form a pair with theIR-ray lamp. Although these gas introducing pipe 33, IR-ray lamp 31 andreflection mirror 32 are shown in the drawing only one for each of them,they are actually provided in number of four at equal intervals,respectively. Of course, these members may be provided in any desirednumber. 34 and 35 are mass flow controllers for controlling the flowrates of the starting gases to be fed into the gas introducing pipe 33and are connected to the gas feeding sources 36, 37, constituted ofbombs, etc. (not shown in the drawing) respectively. In the drawing, thestarting gas feeding system constituted of these mass flow controllersand bombs is made to consist of two systems, but it can also be made toconsist of one system, or two or more systems, as desired.

The drum completed of film formation in the compartment 3 utilizing heatfor film formation is suspended by the hoist 206 to be delivered outagain into the preliminary compartment 2. The drum delivered into thepreliminary compartment 2 is placed on the belt conveyer 203 providedfor durm transfer between the preliminary compartments 2 and 4 and,following the same manner as in transfer between the preliminarycompartments 1 and 2, delivered out into the preliminary compartment 4.

The preliminary compartment 4 is constituted internally similarly to thepreliminary compartment 2, and the drum delivered into the preliminarycompartment 4 is suspended by the hoist 406 similar to that in thepreliminary compartment 2 to be delivered out of the compartment 4 intothe compartment 5 utilizing discharging for film formation.

The drum delivered into the compartment 5 utilizing discharging for filmformation is set on the same heat sink as in the compartment 3 utilizingheat for film formation. Although not explained in the compartment 3utilizing heat for film formation, these heat sink drums are maderotatable as shown by the arrowhead in the drawing for the purpose ofuniformizing the film thickness. The starting gas is introduced throughthe gas introducing pipe 52 into the compartment 5 similarly as in thecompartment 3 utilizing heat for film formation. The starting gasfeeding system for feeding the starting gas to the gas introducing pipe52 is also made to have the same constitution as the compartment 3utilizing heat for film formation.

The starting gas introduced into the compartment 5 is decomposed bydischarging which occurs between the drum and the electrode 51 placedconcentrically outside thereof to form a deposited film on the drum. 54is a high frequency power source for exciting discharging, and 53 is amatching box for applying stable high frequency wave to the electrode51.

The drum completed of film formation in the compartment 5 utilizingdischarging for film formation is delivered out again and into thepreliminary compartment 4. Then, it is transferred into the preliminarycompartment 6 having the same constitution as the preliminarycompartment 1 and delivered out of the system through the door 601.

According to the apparatus provided with the compartment utilizing heatfor film formation and the compartment utilizing discharging for filmformation as shown in the above embodiment and the method by usethereof, formation of a deposited film is possible by utilizing heat anddischarging, respectively. Accordingly, in preparation of an apparatushaving a large area such as an electrophotographic photosensitive memberas mentioned above, film formation may be performed primarily throughutilization of heat which can form a film of good quality at highdeposition speed on a substrate with such a large area, and a film suchas of a-SiC which is formed with difficulty by heat can be formed byutilization of discharging, thus enabling film formations depending onthe properties of the deposited films to be formed, whereby it has beenrendered possible to form an apparatus having more excellent filmcharacteristics than those of the prior art.

In the above embodiment, the substrate is transferred with the use ofpreliminary compartments provided in addition to the compartmentutilizing heat for film formation and the compartment utilizingdischarging for film formation, but provision of such preliminarycompartment or provision of the compartment utilizing heat for filmformation and the compartment utilizing discharging for film formationfunctioning as independent chambers is not necessarily required. Theobject of the present invention can also be accomplished by aconstitution in which the substrate is transferred with the use of agate valve as mentioned above between the compartment utilizing heat forfilm formation and the compartment utilizing discharging for filmformation or a constitution in which the gate valve between thecompartment utilizing heat for film formation and the compartmentutilizing discharging for film formation is removed and the compartmentutilizing heat for film formation and the compartment utilizingdischarging for film formation are allowed to function as one chamber.Of course, depending on various purposes such as improvement ofproductivity, etc., such preliminary compartments may be provided.

In the above embodiment, the substrate used is an aluminum drum forelectrophotographic photosensitive member, but substrates of variousshapes such as plates, cylinders, etc. and various materials may beavailable, Also, concerning the constitution of the compartmentutilizing heat for film formation and the compartment utilizingdischarging for film formation, the above embodiment is not limitativeof the present invention, as a matter of course. In other words,concerning the compartment utilizing heat for film formation, it may beany compartment capable of film formation by decomposition orpolymerization of the starting gas through utilization of heat energy,and any of the various systems known in the art such as gas dischargingsystem, substrate heating system, etc. may be useful. On the other hand,concerning the compartment utilizing discharging for film formation, itmay be any compartment capable of film formation by decomposition orpolymerization of the starting gas through utilization of dischargingenergy, and any of the various systems known in the art such as gasdischarging system, electrode setting system, ect. may be useful. Thesecompartments utilizing heat for film formation and utilizing dischargingfor film formation may be provided in any number, respectively asdesired.

As the starting gas to be used in the present invention as describedabove, most gasifiable substances at normal temperature and normalpressure may be available. For example, gases containing silicon atomsas mentioned above such as SiH₄, (CH₃)₃ Si₂ H₃ can preferably beemployed. Of course, in addition to these gases, doping gas such as B₂H₆, CH₄, etc. and a diluting gas such as Ar, etc. may be used asdesired.

The present invention is described in more detail by referring to thefollowing Examples.

EXAMPLE 1

By means of the apparatus shown in FIG. 1, an electrophotographicphotosensitive member having functional film with three layerconstitution similarly to that shown in FIG. 2 was prepared on analuminum drum.

The aluminum drum was moved in the order of the preliminary compartmentl, the premliminary compartment 2 and the compartment 3 utilizing heatfor film formation successively, and was set in the compartment 3utilizing heat for film formation. After the pressure in the compartment3 was made 0.3 Torr and the temperature of the aluminum 300° C.±10° C.,(CH₃)₃ Si₂ H₃ gas at a flow rate of 100 cc/min. (controlled by the massflow controller 34) and B₂ H₆ gas diluted to 3000 ppm with H₂ gas (B₂ H₆/H₂) at a flow rate of 10 cc/min. (controlled by the mass flowcontroller 35) were permitted to flow thereinto for 5 minutes to form P⁺a-Si layer on the aluminum drum.

Then, the flow of B₂ H₆ /H₂ gas was stopped, with the flow rate of(CH₃)₃ Si₂ H₃ gas being increased to 200 cc/min., and this condition wasmaintained for 3 hours to form non-doped a-Si layer on the P⁺ a-Silayer.

The drum having the above two layers formed thereon was moved in theorder of the preliminary compartment 2, the preliminary compartment 4and the compartment 5 utilizing discharging for film formationsuccessively, and was set in the compartment 5 utilizing discharging forfilm formation. After the pressure in the compartment 5 was made 0.2Torr and the drum temperature 300° C.±10° C., CH₄ gas at a flow rate of100 cc/min. (controlled by the mass flow controller 55) and SiH₄ gas atflow rate of 10 cc/min. (controlled by the mass flow controll 56) werepermitted to flow thereinto, and a high frequency power of 100 W wasapplied. This condition was maintained for 10 minutes to form a-SiClayer on the non-doped a-Si layer.

After formation of the a-SiC layer, the drum was taken out of the systemby moving the drum in the order of the preliminary compartment 4, andthe preliminary compartment 6.

On the drum taken out, uniform films were found to be formed in theorder of A1/P⁺ a-Si 3000 Å/non-doped a-Si 20 μm. The film thicknessesare values when only each of the respective layers was formed under theabove conditions.

This drum was set on a copying machine, and ⊕ 8 KV corona charging,manuscript exposure, development with ⊖ toner, transfer onto paper andfixing were conducted. As the result of evaluation of the imageobtained, excellent image could be obtained.

The image was extremely small in amount of pinholes as compared with theimage obtained by the drum having formed the above three layers onlyutilizing discharging.

EXAMPLE 2

An electrophotographic photosensitive member was prepared in the samemanner as in Example 1 except for using (CH₃)₃ Si₂ H₃ in place of CH₄and SiH₄ as the starting gas for formation in the compartment utilizingdischarging for film formation in Example 1 and changing the appliedvoltage to 60 W.

The drum obtained was set in a copying machine and image evaluation wasconducted similarly to that in Example 1. As the result, an excellentimage was obtained similarly to that in Example 1.

As described above, it has been rendered possible by the presentinvention to form a deposited film by utilizing both decomposition orpolymerization through utilization of heat and decomosition orpolymerization through utilization of discharging. Accordingly, even inthe case of forming various functional films on a large area substratesuch as electrophotographic photosensitive members, etc., depending onthe properties of the film to be formed, for example, it has beenrendered possible to effect film formation primarily through utilizationof heat capable of forming a film of good quality at high depositionspeed on such a substrate, and to form a functional film such as a-SiC,etc., which is formed with difficulty by utilization of heat, byutilizing discharging. Thus, preparation of an apparatus having moreexcellent film characteristics than those of the prior art is nowpossible. Also, in preparation of various functional films, since bothheat and discharging can be utilized, the scope of choice of thestarting materials can be broadened, whereby the respective functionallayers can be formed under the optimum condition.

I claim:
 1. An apparatus for forming a deposited film comprising:a firstcompartment for forming a film on a substrate through thermaldecomposition or polymerization of a starting gas, said firstcompartment having an evacuation means, a starting gas introducingmeans, a substrate holding means, and a heat applying means; a secondcompartment for forming a film on a substrate through dischargedecomposition or polymerization of a starting gas, said secondcompartment having an evacuation means, a starting gas introducingmeans, a substrate holding means, and a dischargae generating means; anda means for delivering a substrate into and out of the first and secondcompartments.
 2. An apparatus according to claim 1, wherein the meansfor decomposing or polymerizing gas by heat is an IR-ray lamp.